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The plasticity and geography of host use and the diversification of butterflies
Stockholm University, Faculty of Science, Department of Zoology.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Our world is changing rapidly and factors like urbanisation, changed agricultural practices and climate change are causing losses in butterfly diversity. It is therefore of importance to understand the source of their diversity. Given the remarkable diversity of herbivorous insects compared to their non-herbivorous sister groups, changes in host use have been implicated as a promoter of speciation. This thesis looks at geographical aspects of host range evolution and the plasticity of host use. We show that butterflies in the subfamily Nymphalinae that feed on a wide range of host plants have larger geographic ranges than species with narrower host ranges. Although tropical butterflies appear to be more specialised than temperate species, this effect is lost when controlling for the differences in geographic range. Geographic variation in host plant use within Polygonia faunus, related to morphologically distinct subspecies, did not show any genetic differentiation. This suggests that the observed variation in host plant use is a plastic response to environmental differences. Reconstructing host use for the Polygonia-Nymphalis and Vanessa group shows that plasticity is also important for understanding host use at the level of butterfly genera. Using unequal transition costs and including larval feeding ability revealed that frequent colonisations of the same plant genus can often be explained by non-independent processes, such as multiple partial losses of host use, recolonisation of ancestral hosts, and parallel colonisations following a preadaptation for host use. These processes are further reflected in the conservative use of host plant orders within the butterfly family Nymphalidae. Few taxa feed on more than one host plant order, and these expansions occur at the very tips of the tree, which we argue is evidence of the transient nature of generalist host use. These insights improve our understanding of how host range evolution may promote diversification.

Place, publisher, year, edition, pages
Department of Zoology, Stockholm University , 2012. , 36 p.
Keyword [en]
Nymphalidae, host range, phylogeny, distribution, latitude, phylogeography, local specialisation, colonisation, host shift, polyphagy, speciation, diversification
National Category
Ecology
Research subject
Animal Ecology
Identifiers
URN: urn:nbn:se:su:diva-69573ISBN: 978-91-7447-440-4 (print)OAI: oai:DiVA.org:su-69573DiVA: diva2:484603
Public defence
2012-03-02, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defence,the following papers were unpublished and had a status as follows: Paper 3: Submitted; Papers 4 and 5: ManuscriptsAvailable from: 2012-02-08 Created: 2012-01-13 Last updated: 2014-10-28Bibliographically approved
List of papers
1. The Relationship between Diet Breadth and Geographic  Range Size in the Butterfly Subfamily Nymphalinae: A  Study of Global Scale
Open this publication in new window or tab >>The Relationship between Diet Breadth and Geographic  Range Size in the Butterfly Subfamily Nymphalinae: A  Study of Global Scale
2011 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 6, no 1, e16057- p.Article in journal (Refereed) Published
Abstract [en]

The ‘‘oscillation hypothesis’’ has been proposed as a general explanation for the exceptional diversification of herbivorous insect species. The hypothesis states that speciation rates are elevated through repeated correlated changes – oscillations – in degree of host plant specificity and geographic range. The aim of this study is to test one of the predictions from the oscillation hypothesis: a positive correlation between diet breadth (number of host plants used) and geographic range size, using the globally distributed butterfly subfamily Nymphalinae. Data on diet breadth and global geographic range were collected for 182 Nymphalinae butterflies species and the size of the geographic range was measured using a GIS. We tested both diet breadth and geographic range size for phylogenetic signal to see if species are independent of each other with respect to these characters. As this test gave inconclusive results, data was analysed both using cross-species comparisons and taking phylogeny into account using generalised estimating equations as applied in the APE package in R. Irrespective of which method was used, we found a significant positive correlation between diet breadth and geographic range size. These results are consistent for two different measures of diet breadth and removal of outliers. We conclude that the global range sizes of Nymphalinae butterflies are correlated to diet breadth. That is, butterflies that feed on a large number of host plants tend to have larger geographic ranges than do butterflies that feed on fewer plants. These results lend support for an important step in the oscillation hypothesis of plant-driven diversification, in that it can provide the necessary fuel for future population fragmentation and speciation.

National Category
Zoology
Identifiers
urn:nbn:se:su:diva-51796 (URN)10.1371/journal.pone.0016057 (DOI)000286511200032 ()
Funder
Swedish Research Council
Available from: 2011-01-12 Created: 2011-01-12 Last updated: 2017-12-11Bibliographically approved
2. Phylogenetic analysis of the latitude-niche breadth hypothesis in the butterfly subfamily Nymphalinae
Open this publication in new window or tab >>Phylogenetic analysis of the latitude-niche breadth hypothesis in the butterfly subfamily Nymphalinae
2010 (English)In: Ecological Entomology, ISSN 0307-6946, E-ISSN 1365-2311, Vol. 35, no 6, 768-774 p.Article in journal (Refereed) Published
Abstract [en]

One possible explanation for the latitudinal gradient in species richness often demonstrated is a related gradient in niche breadth, which may allow for denser species packing in the more stable environments at low latitudes.

The evidence for such a gradient is, however, ambiguous, and the results have varied as much as the methods. Several studies have considered the non-independence of species, but few have performed explicit phylogenetic analyses.

In the present study, we tested for a correlation between diet breadth and latitude of distribution in Nymphalinae butterflies using generalised estimating equations (GEE) and accounting for phylogenetic independence.

Using a simple model with only latitude of distribution as a predictor variable revealed a significant positive relationship with diet breadth. Previous studies, however, have shown that diet breadth is also correlated with butterfly range size, and in turn, that range size may be correlated with latitude of distribution. Including geographical range size in the model also turned out to have a profound effect on the results – to the extent that the relationship between latitude of distribution and diet breadth was effectively reversed.

We conclude that, at least for this group of butterflies, there is no evidence for a positive correlation between latitude of species distribution and diet breadth when controlling for range size, and that the effect may actually even be reversed.

Keyword
Diversification, generalisation, host range, latitude, polyphagy, specialisation.
National Category
Biological Sciences
Identifiers
urn:nbn:se:su:diva-45901 (URN)10.1111/j.1365-2311.2010.01238.x (DOI)000284170200013 ()
Available from: 2010-11-22 Created: 2010-11-15 Last updated: 2017-12-12Bibliographically approved
3. Validity of the subspecies paradigm - a case study of the nymphalid butterfly Polygonia faunus
Open this publication in new window or tab >>Validity of the subspecies paradigm - a case study of the nymphalid butterfly Polygonia faunus
Show others...
(English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203Article in journal (Refereed) Submitted
Abstract [en]

Subspecies are commonly used taxonomic units to formally describe intraspecific geographic variation in morphological traits. However, the concept of subspecies is not clearly defined, and there is little agreement about what they represent in terms of evolutionary units, and whether they can be used as reliably useful units in conservation, evolutionary theory and taxonomy. Although the validity of subspecies has been tested using a multi-marker genetic approach in vertebrates, such studies have been rare in invertebrates. We here test the validity of well-characterized subspecies in the butterfly Polygonia faunus using a combination of mitochondrial sequences and eight microsatellites. We have also investigated the phylogeographic Structure of P. faunus and test whether similarities in host-plant use among populations is related to genetic similarity. Neither the nuclear nor the mitochondrial dataset corroborated subspecies groupings. We found three welldefined genetic clusters corresponding to California, Arizona and (New Mexico + Colorado). There was little structuring among the remaining populations, probably due to gene flow across populations. We found no support for the hypothesis that similarities in host use are related to genetic proximity. The results indicate that the species underwent a recent rapid expansion, probably from two glacial refugia in western North America. The mitochondrial haplotype network indicates at least two independent expansion phases into eastern North America. Ourresults clearly demonstrate that subspecies in P. faunus do not conform to the structuring of genetic variation. More studies on insects and other invertebrates are needed to understand how widespread this phenomenon is. Results in this study will be crucial in designing further experiments to understand the evolution of host plant utilization in this species.

National Category
Zoology
Identifiers
urn:nbn:se:su:diva-71312 (URN)
Available from: 2012-01-27 Created: 2012-01-27 Last updated: 2017-12-08Bibliographically approved
4. Exploring a complex trait - the effect of larval feeding ability and unequal transition costs on the dynamics ofhost range evolution in two groups of related butterflies
Open this publication in new window or tab >>Exploring a complex trait - the effect of larval feeding ability and unequal transition costs on the dynamics ofhost range evolution in two groups of related butterflies
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Host plant use is a complex trait, better described as the combined outcome of many interrelated traits, such as female preference and larval ability to feed, grow and survive. The necessary co-adaptation of these traits would suggest that the host shifts should be difficult to accomplish. Still, even though a large-scale conservatism can be seen in most groups, frequent changes in host use are not uncommon, suggesting that under some circumstances adding new plants to the range might not be as difficult as one might expect. In a case study on two closelyr elated butterfly genera, we investigate the effect of unequal transition costs and of including available data on larval feeding ability as well as plants used in the field, and describe and compare the dynamics of host range evolution in these groups. We find that apparent independent colonisations are in many cases likely to be the result of non-independent processes such as multiple losses, recolonisation or parallel colonisations following some preadaptation. Host plants shifts and range expansions are likely important drivers of the exceptional diversity of herbivorousinsects. A better understanding of the dynamics of host range evolution will improve our understanding of the source of this diversity.

National Category
Ecology Evolutionary Biology Zoology
Identifiers
urn:nbn:se:su:diva-71318 (URN)
Available from: 2012-01-27 Created: 2012-01-27 Last updated: 2012-01-27
5. Host range oscillations in nymphalid butterflies: a phylogenetic investigation
Open this publication in new window or tab >>Host range oscillations in nymphalid butterflies: a phylogenetic investigation
(English)Manuscript (preprint) (Other academic)
Abstract [en]

It has been suggested that phenotypic plasticity is a major factor in the diversification of life, and that variation in host range in phytophagous insects is a good model for investigating this claim. We explore the use of angiosperm plants as hosts for nymphalid butterflies, and in particular the evidence for past oscillations in host range and how they are linked to host shifts and diversification. At the level of orders of plants, a relatively simple pattern of host use emerges, despite the 100 million years of history of the family Nymphalidae. The ancestral host order was very likely Rosales. Later, major host shifts occurred to Gentianales (and even later Solanales) in the Danainae; to Arecales (and even later Poales) in the ”satyrines”; to Malpighiales as the main host order in the ”heliconiines”; and to Lamiales within Nymphalinae. We review the evidence that these host shifts and the accompanying diversifications were associated with transient polyphagous stages, as suggested by the ”oscillation hypothesis” of Janz & Nylin. In addition, we investigate all currently polyphagous nymphalid species (in terms of feeding on more than one host order) and demonstrate that the state of polyphagy is rare and has a weak phylogenetic signal and a very apical distribution in the phylogeny; we argue that these are signs of its transient nature. We contrast our results with data from the bark beetles Dendroctonus, where a more specialized host use is instead the apical state, and suggest that this is simply a stage during a single oscillation when host range is decreasing.

National Category
Ecology Evolutionary Biology Zoology
Identifiers
urn:nbn:se:su:diva-71319 (URN)
Available from: 2012-01-27 Created: 2012-01-27 Last updated: 2012-01-27

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